UNDERSEAT ROCKET MOTOR.- The underseat rocket motor (fig. 5-20) is a sealed unit and consists of a manifold (machined, drilled, and threaded to accept ten propellant tubes), a lateral thrust motor tube, a cartridge tube, and four efflux nozzles. The propellant tubes are

_{Figure 5-21.-Operating controls.}

Figure 5-20.-Underseat rocket motor Mk 123 Mod 0 (forward seat). 5-18

manufactured from seamless steel. The tubes contain solid propellant drilled lengthwise through the center and having three equally spaced ribs to provide rapid and even burning. A cross-shape grid is positioned between the propellant and the manifold to ensure that the gas generated can pass unrestricted to the manifold. The cartridge tube is internally threaded to accept a gas-operated igniter cartridge incorporating twin firing pins and twin primers. A lateral thrust motor with an integral cartridge is screwed into the manifold at the LH end (forward seat) or RH end (aft seat). The efflux nozzles are fitted under the manifold and are sealed at the inner end by flanged blowout discs, which cause a pressure build-up to ensure rapid and even burning of the propellant and an even thrust from the motor. Threaded holes in the manifold end plugs and a steady bracket clamped to the lateral thrust motor are used to secure the motor under the seat bucket, The threaded holes in the manifold end plugs vary in size between forward and aft seats to ensure location in the correct cockpit.

LATERAL THRUST MOTOR.- The lateral thrust motor (fig. 5-20) forms an integral part of the main rocket motor, being screwed into the manifold. An igniter cartridge is initiated by gas pressure from the rocket motor propellant and ignites the propellant in the lateral thrust motor to permit a divergent trajectory to the ejected seat.

EJECTION CONTROL HANDLE.- The ejection control handle (figs. 5-21 and 5-22) is located on the front of the seat bucket. It is the only means by which ejection can be initiated. The handle is molded in the shape of a loop, and is connected to the sears of the ejection seat initiators. The seat initiators have two rigid lines that connect to the trombone fittings. An upward pull of the loop removes both sears from the dual initiators to initiate ejection. Either initiator can fire the seat. After ejection the handle remains attached to the seat. The ejection control handle is safetied by using the ejection seat safe/arm handle and safety pin.

Figure 5-22.-Ejection control handle. 5-19

Figure 5-23.-Locations of safety devices.

SAFE/ARMED HANDLE.- The SAFE/ARMED handle (figs. 5-21 and 5-23) is located on the RH side of the seat bucket immediately forward of the emergency restraint release handle. Contained within the handle is a catch that locks the handle in either the ARMED or SAFE position. The handle is connected to a linkage that terminates in a safety plunger, which passes through the link of the ejection control handle when the handle is in the SAFE position and prevents operation of the ejection control handle. When in the ARMED position, the visible portion of the handle is colored yellow and black stripes and engraved ARMED; when in the safe position, the visible portion is colored white and engraved SAFE. An electrical visual SAFE/ARMED indicator is incorporated in the cockpit central warning panel, and is operated by a microswitch actuated by the safety plunger.

LEG RESTRAINT SNUBBERS.- Two leg restraint line snubbers (fig. 5-24), each with a leg restraint line, are attached to the front face of the seat bucket. Release of the leg restraint line snubbers to adjust the leg lines is effected by pulling inboard on the fabric loops attached to the release plungers on the inboard side of each snubber. The leg restraint lines taper plugs are secured in locks positioned on the seat bucket side plates.